I`m in a 1930s built ex-council house, and the walls upstairs are made of
some horrendously soft material (compressed ash I think)
You can use these:
http://tinyurl.com/rz9w
Which you drill a hole just smaller than the diameter of the fixing and then
screw the anchor into the hole. These are meant for plasterboard fixing but
are great on soft thermal block and ash block like you have, as well.

Sounds promising - thanks for the replies guys :-)

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